Methods for Obtaining X-Ray Diffraction Patterns from Drosophila 198 Diffraction Patterns from Drosophila IFM 203 Concluding Remarks 211 Note Added in Proof 211 17. Functional and Ecological Effects of Isoform Variation in Insect Flight Muscle 214 James H. Marden Abstract 214 Introduction 215 Nature's Versatile Engine 215 The Underlying Genetics: An Underinflated Genome and a Hyperinflated Transcriptome and Proteome 216 Functional Effects of Isoform Variation 219 Alternative Splicing and the Generation of Combinatorial Complexity 220 Functional Consequences of Naturally Occurring Isoform Variation 220 18. Muscle Systems Design and Integration 230 Fritz- OlafLehmann Abstract 230 Power Requirements for Flight 230 Power Reduction 233 Power Constraints on Steering Capacity 234 Balancing Power and Control 236 Changes in Muscle Efficiency in Vivo 238 Concluding Remarks 239 From the Inside Out 19. Molecular Assays for Acto-Myosin Interactions 242 John C. Sparrow and Michael A. Geeves Abstract 242 Introduction 242 Myosin Purification and Preparation of the SI Fragment 243 Purification of Flight Muscle Actin 244 Assays of Myosin and Acto-Myosin 244 Major Conclusions Relating to the Enzymatic Properties of Insect Flight Muscle Acto-Myosin 247 Major Questions about Insect Flight Muscle Acto-Myosin Kinetics That Remain 249 20.